InterPore2026

Effect of metakaolin and fly ash on the early hydration and pore structure of Portland cement

19 May 2026, 15:05

1h 30m

Poster Presentation (MS13) Fluids in Nanoporous Media Poster

Speaker

Dr Vanda Papp (University of Debrecen, Department of Physical Chemistry)

Description

When conditioning radioactive waste, enhancing the sorption properties of binders is essential. This can be accomplished through the use of various additives, such as artificial silicates. However, these additives can significantly affect the mineral composition of the cement and, consequently, alter its pore structure, including the size and distribution of the pores.
The aim of this work was to comprehensively describe the effects of two pozzolanic materials - metakaolin and fly ash - on the early hydration, structural development, and hardened pore structure of Portland cement. A novel combination of NMR methods, scanning electron microscopy (SEM), and N₂ porosimetry was applied. The early hydration processes in the pozzolan-containing cement composites were monitored using low-field NMR relaxometry, which showed that metakaolin exhibited pozzolanic activity after 8 hours, while filler effect was observed for fly ash. Fast field cycling NMR relaxometry and T₁-T₂ correlation relaxation measurements revealed a stronger interaction between water and the solid for the composites compared to pure cement. NMR relaxometry and N₂ adsorption demonstrated that the dominance of the small pores in the CSH gel increased with the additives. Water diffusion in the capillary pores, followed by H₂O- D₂O exchange diffusion, was slower in metakaolin composites than in fly ash containing samples.
Overall, replacing cement with fly ash resulted in the formation of a porous structure where the contribution of the micropores and the bound water types is significant, beside the presence of macropores. In contrast, the addition of metakaolin enhanced the micro- and mesoporous nature of the cement, which led to a less permeable, more homogenous and contiguous solid matrix, being advantageous for the long-term safe disposal of radioactive waste.